In displays and HDTV (High Definition TeleVision) broadcasting, color spaces standardized by sRGB (IEC (International Electrotechnical Commission) 61966-2-1) or ITU-R (International Telecommunication Union-Radiocommunication Sector) BT.709 have been widely used. In recent years, with the advent of wide color gamut panels, color representations of a wider color gamut exceeding sRGB are now possible on the TV receiver side.
To make full use of a wider color gamut of panels, such a TV receiver adopts a technology to expand the color gamut (hereinafter, called “color gamut expansion processing”) by signal processing on video content of the color space of sRGB and the TV receiver can reproduce more vivid colors by performing color gamut expansion processing of colors with saturation at such a high level that would be clipped in the sRGB color space. Moreover, the user can turn on/off color gamut expansion processing by selecting the image quality mode of the TV receiver.
The TV receiver can also receive color space information from a source device together with a video signal by using HDMI (High-Definition Multimedia Interface) and exercise control according to color space information such as turning on color gamut expansion processing for BT.709 and turning off color gamut expansion processing for color space information of other wide color gamut automatically.
On the other hand, image sensors and camera signal processing increasingly adopt the wide color gamut and a wide color gamut signal of the color gamut that is shot by a camera and exceeds that of sRGB can be recorded on a disk or tape before being reproduced. The wide color gamut signal recorded on a disk or tape can also be dubbed onto an optical disk recorder via a digital interface such as IEEE (Institute of Electrical and Electronic Engineers) 1394 or the disk on which a wide color gamut signal is recorded can be reproduced by an optical disk recorder or player. Moreover, a camera and recorder can transmit such a wide color gamut signal or color space information to a TV receiver by using HDMI.
A conventional display using a CRT (cathode ray tube) can display only colors, for example, inside the color space covered by sRGB and it is difficult to see colors with high saturation present in the natural world through the display. However, displays having a wider color gamut than before are appearing thanks to recent display technology and a liquid crystal TV receiver using an LED (light emitting diode) backlight is known as a typical wide color gamut compatible display.
xvYCC is standardized as a standard for video signal (image signal) suitable for such a wide color gamut display after video signal specifications that adopt a wide color gamut while maintaining compatibility with conventional signals being discussed. The xvYCC is a standard issued by IEC (International Electrotechnical Commission) as an international standard (IEC 61966-2-4) and broadens the color space while ensuring compatibility with the color gamut of ITU-R BT. 709 (equivalent to sRGB) used by HDTV (High Definition TeleVision). According to the xvYCC, colors that is difficult for the current color space standard “ITU-R BT.709” (equivalent to sRGB for still images) of animation content can be represented.
For transmission using a wide color gamut such as the xvYCC, it is necessary for both a sender and a receiver to recognize that an xvYCC signal is transmitted and make a correct display because the color space of the sender and that of the receiver may be different. Thus, for example, color space information can be received together with a video signal from the source device by using HDMI and definitions of metadata and the xvYCC color space are added to the HDMI version 1.3.
That is, while only the color space of SMPTE 170M/ITU601 or ITU709 was defined before in AVI (Auxiliary Video Information) InfoFrame as attribute data of the HDMI standard, a field is now added for a new color space such as xvYCC. When an xvYCC signal is transmitted by between devices compatible with the HDMI version 1.3, correct gamut mapping between a sender and a receiver can be realized by supporting the standard.
Patent Document 1 discloses a technology enabling desired color reproduction by using a standard color space whose color gamut is expanded as conventional technology.